This study investigated parental perception of sleep problems in stimulant treated and untreated children with Attention Deficit Hyperactivity Disorder (ADHD). Parents of 135 psychiatric clinic referred children and 83 pediatric outpatients completed a sleep questionnaire and the Child Behavior Checklist. Moderate to severe "sleep problems" reportedly occurred at least once a week in 19.3% of children with ADHD, 13.3% of the psychiatric controls, and 6.2% of the pediatric controls. Children with ADHD treated with stimulants were reported to display a higher prevalence of nightly "severe" sleep problems than did untreated children with ADHD. Almost a third (29%) of stimulant treated ADHD children were reported to display increased sleep latency or insomnia every night versus 10% of untreated children with ADHD. Despite the high prevalence of sleep related problems in ADHD, the significance of the association between delayed sleep onset and ADHD with regard to etiology and management of ADHD is still poorly understood.